Transformer of the constant or limited current type



Aug. 20, 1940. SQLA 2,212,198

.TRANSFORNER OF THE CONSTANT OR LIMITED CURRENT TYPE Filed Marqh 25, 1940 2 Sheets-Sheet 1 Aug. 20, 1940. J. G. SOLA 2,212,198

' TRANSFORMER OF THE CONSTANT 0R LIMITED CURRENT TYPE Filed March 25, 1940 2 Sheets-Sheet 2 D CURREN'P-AMPERES 7 @6754??? 3L 0000 .4 7. 52 1, k I00 no H5 as: [as I a l/ Vfl-TS 5 E K2 9 6 59 @k (A), M

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Patented Aug. 20, 194% UNITED STATES TRANSFORMER OF THE CONSTANT R LIMITED CURRENT TYPE Joseph G. Sola, Oak Park, Ill., asslgnor to Sola Electric 00., Chicago, 111., a corporation of Delaware Application March 25, 1940, Serial No. 325,720

' 10 Claims. (01. 171-119) My invention relates to an improved transformer arrangement of the constant or limited current type. My invention in certain respects is related to the transformer arrangements shown and described in my Patent No. 2,143,745, issued January 10, 1939.

It is an object of my invention to provide an improved transformer arrangement of the type having a constant or limited output current characteristic and which with any certain load has an output current that remains substantially constant irrespective of variations of the primary or input voltage to the arrangement.

It is another object of my invention to provide an improved transformer arrangement of the type having a constant or limited output current characteristic, the efilciency and power factor of which are high while the temperature rise of the magnetic core is low.

It is a further object of my invention to provide an improved transformer arrangement of the type having a constant or limited output current characteristic and which comprises a single unit and may be economically manufactured.

It is also an object of my invention to provide an improved transformer arrangement of the type having a constant or limited output current characteristic and which comprises two windings loosely coupled together magnetically and a condenser, one of the windings being a load winding and the other being a primary winding with respect to theload winding and forming with the condenser a resonant circuit.

The invention consists of the novel constructions, arrangements, and devices to be hereinafter described and claimed for carrying out the above stated objects and such other objects as will appear from the following description of '40 certain preferred embodiments illustrated in the accompanying drawings, wherein,

Fig. 1 is a transformer unit embodying the principles of my invention;

Fig. ,2 is a diagrammatic illustration of one form of wiring arrangement that may be used with the transformer unit shown in Fig. 1;

Figs. 3, 4 and 5 are diagrammatic illustrations of modified forms of transformer arrangements, embodying the principles of my invention, that may be used with magnetic cores such as that of the transformer unit shown in Fig. 1; and

Figs. 6 and 7 are graphs showing the operating characteristics typical of transformers embody- 55 ing my improvements.

Like characters of reference designate like parts in the several views.

Referring to Figs. 1 and 2, it will be seen that a core type of transformer construction is illustrated, the closed magnetic circuit ID of which 5 comprises a stack of I-shaped laminations forming a straight core bar H and a stack of laminations which form a magnetic return path 12 in the form of an inverted U or yoke disposed with its end legs 12a in abutting relation with '10 the core bar II. The laminations may be held together by any suitable means.

On the end portion A of the core bar II, I have provided a primary or input winding IS, the terminals l4 and I5 of which are adapted 15 to be connected with a source of alternating current, the voltage of which from time to time may fluctuate or vary substantially. On the central portion B of the core bar II, I have mounted what may be termed an intermediate m winding 16, which is in spaced relation to but magnetically coupled with the winding 13, the winding l6 having terminal leads Hand 18. A condenser I9 is connected between the leads I! and I8 and thereby across the winding 16 for 25 purposes hereinafter to be described. On the end portion C of the core bar, I have mounted a winding 20 having terminal leads 2| and 22. The winding 20 may be termed a load winding and is spaced from but is magnetically coupled 30 with the winding 16.

The magnetic circuit 10 is provided with a high leakage reactance path 12b between the windings l3 and I8 and a high leakage reactance path 120 betweenthe windings I6 and 20. The 5 paths I21) and l2c comprise central, inwardly extending legs of the magnetic return path l2 which terminate short of the core bar I 1 thereby providing non-magnetic or air gaps 23. The paths I21) and 120 are magnetically permeable 40 shunts, each having a non-magnetic gap portion, and are so arranged that magnetic flux may thread each of the windings I3, I6 and 20 to the exclusion of the other windings.

The transformer arrangement shown in Fig. 3 is provided with a magnetic core similar to the core 01' the Fig. 1 arrangement. In this Fig. 3 arrangement, the load winding 20 is connected by its terminal lead 21a in series with an auxiliary winding 24 having a terminal lead 25, the winding 24 being wound on the portion A of the core bar H and closely coupled magnetically with the input winding 13.

The transformer arrangement of Fig. 4 also comprises a magnetic core similar to that of the Fig. 1 transformer. In this Fig. 4arrangement, the windings i3 and I6 are connected together .with an auto type of connection, the condenser I9 being connected between the leads I8 and I 4 and across the windings I3 and I6, and the lead I1 is connected to the lead I6, thereby connecting the windings =I3 and IS in series. In other respects, the wiring arrangement is similar to that of Fig. 3.

' 10 The transformer arrangement shown in Fig. 5

may also comprise a magnetic core and windings similar to the Fig. 1 transformer. In this Fig. 5 arrangement, however, the windings 13 and 16 are connected together with an auto type 16 of. connection, and the winding [6 is also connected to the winding 20 with an auto type of connection. The condenser I9 is connected between theleads I8 and II and across the windings I3 and I6, and the lead I! is connected 20 to the lead I5, thereby connecting the windings I3 and I6 in series. The winding 20 is connected with the winding I6 by the terminal lead 2") which is connected to an intermediate tap 26 of. the winding I6.

- In my several transformer arrangements, VP

represents the voltage applied across the input or primary windings I3; V1 represents the voltage across the intermediate windings I6; VL represents'the voltage across the load windings 20;

80 and V0 represents the output voltages; V0 and V1. being the same in the Fig. 2 arrangement.- In

the arrangements of Figs. 3 and 4, VA represents the voltage across the auxiliary windings 24.

'The principles upon which my improved trans- 85 formers operate will be clear from a detailed consideration of the arrangement shown in Figs.

1 and 2. A voltage VP from an external source is applied across the primary winding I3 causing current to flow through the winding l3 setting 40 up magnetic flux in the core portion A. The

' gwindings I3 and I6 are magnetically coupled and the flux set up in the core portion A makes a circuitthrough the core bar II and magnetic return path I2 and links the winding I 6. This 45, flux causes a definite reaction and voltage to be set up in the winding I6. As the voltage VP on the primary winding I3 is increased from zero to a higher level, the flux threading the winding I6 tends to increase in nearly direct proportion to the primary flux. Due to the reluctance of the air gaps 23, only a slight amount of flux leaks through the shunts I21) and I2c. As the induced E. M. F. reaches a higher value in winding I6, a critical point is reached where resonance takes place, and then the reactance of. the effective inductance of the winding I6 and the capacity reactance of the condenserIS are approximately equal, that is to say,

where f is the frequency of the voltage impressed on the primary winding I3, L is the effective inductance of the winding I6 and C is the capacity of the condenser I9. Under this resonant condition, a definite amount of current will flow in the resonant circuit, comprising the winding I6, condenser I9 and leads I1 and I8; and such current will be limited by the constants of that circuit,

and the result is that a. potential V: will be set up across the winding I6 and a corresponding amount of magnetic flux will be set up in the centenportion B of the core bar II.

When the circuit comprising the winding I6 and the condenser I9 is in resonance, the magnetic density of the core portion B is greater than the magnetic density in the core portion A. As

increases, but the magnetic density-in the core 5 v portion B stays substantially the same and increases only slightly since more and more flux is -by-passed through the shunt lib. Thevoltage V1 across the winding I6 also stays substantially the same and increases only slightly with a corre- 1 sponding slight increase of magnetic fiux density in the core portion B. Due to the passage of flux, created by the flow of current in the primary winding I3, through' the shunt I2b to the ex'clusion of winding IS, the coeflicient of coupling 15 between the primary winding l3 and the intermediate winding I6 is at a reduced value, and a balanced condition is maintained as the voltage VP is varied in a range above its critical value such that the resonant circuit will continue to go oscillate with substantially a maximum current therein at a frequency equal to the frequency of the voltage impressed on the primary or input winding I3.

When the winding 20, which is magnetically g5 coupled with the winding I6, is open and has no load connected between its terminals 2i and 22 substantially all the magnetic flux in the core portion B also threads the portion C of the core,

" and substantially none of the magnetic flux in so the portion 13 passes through the shunt I20. However, when a load, such as a gaseous discharge tube 21, is connected between the terminals 2| and 22 of the winding 20, the magnetic flux density in the core portion C decreases. Some oi the magnetic flux in the core portion B now passes through the shunt I20 to the exclusion or winding 20. The voltage V0, therefore, with the load 21 between the terminals 2i and 22 is less than the voltage V0 with no load between 40 said terminals. With a load current flowing in the winding 20, there is a tendency for the magnetic flux density in the core portion B and the voltage V: to decrease from their no load values since the windings I 6 and 20 are magnetically 45 coupled and the load on winding 28 is reflected to the resonant circuit. However, the arrangement is such that on the application of a load across the winding 20, more current flows through the primary winding I3, and the net 50 result is that the magnetic flux density in the core portion B and the voltage V: remain substantially the same.

A load of substantially any impedance or one which varies in impedance may be put between 55 the terminals 2| and 22 of the winding 20, and the terminals 2| and 22 may even be shorted together without an excessive flow of current in the winding 20. The magnetic flux in the core "portion B either passes through the shunt I 2b, 5

to the exclusion of the winding 20, or else threads the winding 20. That portion of the magnetic flux passing through the shunt I2c produces a self-inductive efiect in the winding I6, while the flux which passes through the core portion C 65 and through the winding 20 results in the production of secondary current in the winding 20. Any tendency to increase the load current in the winding 20 will at once be followed by increased self-induction of the winding 20 due to the in.- 7 creased flow of magnetic flux from the winding 20 through the shunt I20, and at the same time the self-induction of the winding It will also increase owing to theincreased amount of flux from the winding 16 flowing through the shunt 75 |2c. The eflect of the increased sell-induction of winding 20 due to an increase in current in the winding is to choke or turn back the magnetic flux lines tending to pass through the winding 20 from the winding |6and to cause these flux lines to be shunted through the shunt l2c. A varying impedance in the circuit of the load winding 20, therefore, receives a current which tends to be limited in strength and to be selfregulated. when there is a high impedance load between the terminals 2| and 22 oi the winding 20 nearly all the magnetic flux in the core portion 13 passes through the winding 20 and the voltage V0 is at a high value but when the impedance of the load is decreased substantially such that a much larger load current would flow with the same V0, then a much smaller portion of the magnetic flux threading the winding I6 passes through the winding 2|! and the voltage Vo, therefore, decreases substantially such that the load current remains the same or only rises slightly. When the leads 2| and 22 are shorted together the voltage V0 is substantially zero, but the current through the winding 20 either remains constant or increases only slightly since most of the flux passing through each of the windings l6 and 20 passes-through the shunt |2c to the exclusion of the other winding. With this arrangement there is no danger of an excessive flow of current through the winding 20 causing it to burn out.

In short, the winding l3 operates as a primary winding with respect to the winding l6 and, due to the presence of the shunt |2b between them, the windings l3 and I6 are loosely coupled together, and the circuit comprising the winding I6 and the condenser l9 resonates at the frequency of the voltage V? applied to the input winding l3 when the voltage VP is above a certain critical value. The winding l6 operates as a primary winding with respect to the winding 20, and, when there is no load between the terminals 2| and 22 of the winding 20, the magnetic coupling between the windings l6 and 20 is substantially unity, but when a; decreasing load is present between the terminals12| and 22 tending to cause an increasing flowof current in the winding 20 thef magnetic coupling between the windings I6 and p2ll decreases. The voltage V1 across the winding l6 remains substantially the same regardless of the load between the terminals 2| and 22 of the winding 20- and the voltage V: increases only slightly with an increase of Vp; the winding I6 is in effect then a constant voltage primary winding with respect to the winding 20.

In the Fig. 3 arrangement, an auxiliary winding 24 closely coupled with the primary winding I3 is connected in series with the load winding 20. As has been noted heretofore the voltage V1 increases slightly upon an increase of voltage V1, and V1. and VA also increase. with the auxiliary winding 24, substantially no increase of current through or voltage across a constant load between the leads 22 and 25 will take place upon an increase of the voltage VP. The number of turns in the winding VA is such that, upon an increase of voltage VP, the vectorial difference between the voltages V1. and VA stay substantially the same and this voltage difierence is the voltage V0; and since V0 is constant, the current flowing through the load 21 also remains substantially the same.

Inthe Fig. 4 arrangement, the voltage V1? is impressed across both windings l3 and |6,and the winding I6 is caused to resonate not only by the magnetic flux from the winding I3 but also due to the voltage VP impressed across the winding l8.

In the Fig. 5 arrangement, the winding. I6 is caused to resonate as in Fig. 4 arrangement and the output voltage Vo taken between the leads I8 and 22 is the sum of the voltage Vr. across the winding 20 and the voltage across that portion of the winding l6 betweenthe leads l8 and-the tap 26.

The graph in Fig. 6 shows the manner in which the input power factor and the load current of a certain embodiment of my Fig. 3 transformer arrangement varies with the input voltage Vr, the load being substantially constant and of unity power factor. It will be noted that the input power factor is substantially unity and that the load current is substantially constant as V? increases. The graph in Fig. 7 show the manner in which the output voltage V0 of the embodiment aforesaid decreases with a constant V? on a decrease of load impedance as the output current increases to a limit or constant value, the limit in this case being 4 amperes at short circuit of leads 22 and 25. Results approximating those shown in the graphs of Figs. 6 and 7 are obtained with the other forms of my invention described herein.

My improved transformer arrangements are of the high reactance type and are particularly suitable for use with mercury vapor lamps, neon electric discharge tubes, or other loads having a negative resistance characteristic. My transformer arrangements constitute electric supplies which substantially decrease in output voltage on the passage'of an increased amount of current from the arrangements to their loads, this being the type of electric supply required to operate satisfactorily loads having a negative resistance characteristic, and my transformer arrangements are such that variations of input voltage to the arrangements have substantially no eifect on the voltage across or the current through the loads. Each of my improved transformer arrangements consists of only a single unit which may be economically manufactured. The temperature rise in the magnetic cores of my arrangements is low, and the efliciency thereof is high.

I wish it to be understood that my invention is not to be limited to the specific constructions shown and. described, except so far as certain of the claims may be so limited, as it will be apparent to those skilled in the art that changes in the constructions and arrangements may be made without departing from the principles of my invention.

I claim:

1. In a transformer of the type described, the combination of a magnetic core having thereon an input winding adapted to be connected to a source of alternating current of fluctuating voltage, an intermediate winding on said core magnetically coupled with said input winding, a load winding on said core magnetically coupled with said intermediate winding, said core providing high leakage reactance paths magnetically between said windings for flux to thread through each of the windings to the exclusion of the other windings, and a condenser connected across at least said intermediate winding and forming therewith a resonant circuit for maintaining the voltage across the intermediate winding substanlimited current supply.

. 2. In a transformer 01' the type described, the

combination of a magnetic core having thereon an input winding adapted to be connected to a source of alternating current of fluctuating voltage, an intermediate winding on said core magnetically coupled with said input winding, a loadwinding on said core magnetically coupled with said intermediate winding, said core providing a magnetically permeable shunt magnetically between said input and intermediate windings and a magnetically permeable shunt magnetically between said intermediate and load windings, each of said shunts having a non-magnetic gap portion, and a condenser connected across at least said intermediate winding and forming therewith a resonant circuit for maintaining the voltage across the intermediate winding substantially constant, said load winding serving as a limited current supply.

8. In a transformer oi the type described, the combinationof a magentic core having a straight core portion, an input winding on said core portion adapted to be connected to a source of alternating current of fluctuating voltage, a load winding on said core portion, an intermediate winding'on said core portion between the input and load windings, said core providing high leakage reactance paths between said windings for flux to thread through each of the windings to the exclusion of the other windings, and "a condenser connected across at least said intermediate winding andforming therewith a resonant circuit for maintaining the voltage across the intermediate winding substantially constant, said load winding serving as a limited current supply.

4. In a transformer of the type described,the combination of a magnetic core having a straight 'core portion, an input winding on said core por-' tion and adapted to be connected to a source of alternating current of fluctuating voltage, a load winding on said core portion, an intermediate winding on said core portion between the input and load windings, said core'provldingbetween said input and intermediate windings and between said intermediate and load windings magnetically permeable shunts each having a nonmagnetic gap portion, and a condenser connected across at least said intermediate winding and tween said windings for flux to thread through each of the windings to the exclusion of the other windings, a condenser connected across at least said intermediate winding and forming therewith a resonant circuit for maintaining the voltage across the intermediate winding substantially constant, and an auxiliary winding closely coupled magnetically with said input winding and connected in series with said load winding and serving with the load winding as a limited current supply.

r 6. In a transformer of the type described, the

' combination of a magnetic core having thereon an input winding adapted to be connected to a source oi! alternating current of fluctuating voltage, an intermediate winding on said core magnetically coupled with said input winding. a load winding on said core magnetically coupled with said intermediate winding, said core providing a magnetically permeable shunt magnetically between said input and intermediate windings and a magnetically permeable shunt magnetically between said intermediate and load windings, each of said shunts having a non-magentic gap portion, a condenser connected across at least said intermediate winding and forming therewith a resonant circuit for maintaining the voltage across the intermediate winding, substantially constant, and an auxiliary winding closely coupled magnetically with said input winding and connected in series with said load winding and serving with the load winding'as a limited current supply.

"I. In a transformer 01' the type described, the combination of a magnetic core having a straight core portion, an input winding on said core portion adapted to be connected to a source of a1- ternati.ng current of fluctuating voltage, a load winding on said core portion, an intermediate winding on said core portion between the input and load windings, said core providing high leakage reactance paths between said windings for flux to thread through each of the windings to the exclusion of the other windings, a condenser connected across at least said intermediate winding and forming therewitha resonant circuit for maintaining thervoltage across the intermediate winding substantially constant, and an auxiliary winding on the core in inductive relation to said input winding and connected in series with said load winding and serving'with the load winding as a limited current supply.

8. In a transformer of the type described, the combination of a magnetic core having thereon an input winding adapted to be connected to a source of alternating current of fluctuating voltage, an intermediate winding on said core connected with and magnetically coupled with said input winding, a load winding on said core magnetically coupled with said intermediate winding, said core providing high leakage reactance paths magnetically between said windings for flux to thread through eachof the windings to the exclusion of the other windings, and a condenser connected across said intermediate wind-.

ing and across at least a portion of said input winding and forming with the intermediate winding and the connected portion of the input winding portion a resonant circuit for maintaining the voltage across the intermediate winding substantially constant, said load winding serving as a limited current supply.

9. In a transformer of the type described, the combination of a magnetic core having thereon an input winding adapted to be connected to a source of alternating current of fluctuating voltage, an intermediate winding on said core magnetically coupled with said input a load winding on said core magnetically coupled with said intermediate .winding, said core, providing high leakage reactance paths magnetically between said windings for flux to thread through each of the windings to the exclusion of the other windings, and a condenser connected across at least said intermediate winding and forming therewith a resonant circuit for maintaining the voltage across the intermediate winding substantiaily constant, said load winding being connected with said intermediate winding and serving with the connected portion of the intermediate winding as a limited current supply.

10. In a transformer of the type described, the combination of a magnetic core having thereon an input winding adapted to be connected to a source of alternating current of fluctuating voltage, an intermediate winding on said core connected with and magnetically coupled with said input winding, a load winding on said core magnetically coupled with said intermediate winding, said core providing high leakage reactance paths magnetically between said windings for flux to thread through each of the windings to the exclusion of the other windings, and a condenser connected across said intermediate winding and across at least a portion of said input winding and forming with the connected portion of the input winding and the intermediate winding a resonant circuit for maintaining the voltage across the intermediate winding substantially constant, said load winding being connected with said intermediate winding and serving with the connected portion of the interme- 1o diate winding as a limited current supply.

JOSEPH G. SOLA. 

